A multitude of molded parts are used in the interior of vehicles, for example door panels, roof linings, dashboards or instrument panels. The substrate of the molded part is made of plastic or preferably of a fibrous molding material, realized in a laminar fashion and has an essentially plane contour or a three-dimensional contour with convex and concave regions defined by the respective design, as well as, if applicable, one or more openings and recesses for trim strips and control elements such as pushbuttons, switches and rotary knobs for power windows and exterior rearview mirrors. In order to fix the molded parts in the passenger compartment or on the vehicle door and to mount handles, control elements and storage trays on the molded part, the molded part is also equipped with mounting parts that among experts are also referred to as retainers.
The substrate typically consists of plastics or composite materials that contain plastics such as acrylonitrile-butadiene-styrene (ABS) or polypropylene (PP). Fibrous molding materials on the basis of textile fabrics of hemp, sisal, flax, kenaf and/or wood components such as wood fibers, wood dust, wood chips or paper bound with duroplastic binders are likewise used as material for the substrate. Foamed materials of polyurethane or epoxy resins that, if applicable, are reinforced with natural fibers or glass fibers may also be considered as material for the substrate.
The side of the respective molded part or substrate that faces the vehicle interior is usually referred to as the visible side. In order to provide the visible side with an attractive appearance, the substrate is equipped with one or more decorative elements of a textile material or a plastic film. The plastic films used for this purpose are usually colored and have a relief-like embossed surface. If applicable, the decorative elements comprise a cushioning layer of a foamed plastic that faces the substrate and provides the molded part with pleasantly soft haptics. The decorative elements are usually laminated onto the substrate or bonded thereto during the manufacture of the substrate by means of thermoplastic back-injection molding.
On its edge and/or on an installation side that lies opposite of the visible side, the substrate is advantageously equipped with projections, depressions and bores. The projections, depressions and bores serve for non-positively connecting the molded part to sections of the car body such as a car door or the roof of a passenger compartment by means of retaining elements such as clips, pins and screws.
The respective mounting parts or retainers are made of plastic or a metallic material such as sheet steel and mechanically connected to the substrate by means of retaining elements such as pins, screws or clips or by means of interlacing, clawing or clamping. Retainers advantageously comprise claws and/or clips as integral components. The claws and clips are respectively provided for engaging into recesses of the substrate or for being bent around the edge of the substrate, as well as for being fixed by means of clamping, during the installation of the retainers.
Different methods that typically comprise two or more production steps are known for the manufacture of molded parts for the interior trim of vehicles.
According to one known method, a substrate is initially produced of a fibrous molding material by means of hot-pressing. Subsequently, retainers are attached to the installation side of the substrate, e.g., by means of friction welding or bonding. In a third step, one or more decorative elements are laminated onto the visible side of the substrate. In a simplified two-step variation of the method, retainers of a metallic material with integrated retaining elements, particularly with claws, are compressed together with the fibrous molding material, wherein the retaining elements penetrate into the fibrous molding material and non-positively anchor the retainers on the substrate after the fibrous molding material has cured.
According to another known method, a substrate is manufactured of a thermoplastic by means of injection molding, particularly by means of back-injection molding. One or more decorative elements are preferably arranged in a back-injection mold and back-injected with the thermally plasticized plastic. After the molten plastic has cooled and solidified, the decorative elements are non-positively bonded to the substrate. In another step, mounting parts or retainers are respectively mounted on the installation side of the substrate.
Substrates of fibrous molding material are utilized for the interior trim of vehicles to a continuously increasing extent. Fibrous molding materials have a few advantages over plastics. For example, a considerable portion of fibrous molding materials is produced of renewable resources such as conifers, hemp or kenaf. Technical and economical considerations also fuel the trend toward fibrous molding materials. At the same specific rigidity, fibrous molding materials have a lower weight than glass fiber-polypropylene composites or talcum-polypropylene composites. Substrates of fibrous molding materials are distinguished by their favorable crash and splintering characteristics, their sound energy and acoustic absorption (also at cold temperatures) and a comparatively low coefficient of thermal expansion. The industry has many years of experience with the processing of fibrous molding materials, wherein the corresponding processes and hot-pressing molds are respectively robust and cost-efficient in comparison with injection molds. Fibrous molding materials allow the manufacture of substrates with highly pronounced undercuts and changes in direction with an angle of up to 180 degrees. Furthermore, wood fibers and natural fibers are available in large quantities, wherein their prize is also less dependent on the price of crude oil than petroleum-based plastics.
One example of a surface texture is disclosed in WO 2010/080967 A1, according to which an interior trim panel of fibrous molding material is equipped with a smooth, transparent, liquid-impermeable, scratch-resistant and UV-resistant coating of a material, preferably a thermoplastic polymer, with a melting point in the range of 60 to 170° C. The coating is applied by means of hot-pressing, wherein the material of the coating partially sinks into the fibrous molding material such that the coating is non-positively connected to the fibrous molding material.